docs: def _find_plugin_dir(module_type):
      '''Find the directory containing the plugin definition for the given type.
      Do this by searching all the paths where plugins can live for a dir that
      matches the type name.'''
  
      for install_dir in _get_plugin_install_dirs():
          candidate = os.path.join(install_dir, module_type)
          if os.path.isdir(candidate):
              return candidate
      else:
          raise PluginCandidateError(
              'No plugin found for `{}` module in paths:\n{}'.format(
                  module_type, '\n'.join(_get_plugin_install_dirs())))